you're supposed to back the bells and birfs with axle grease if they put 90 weight in there, they are going to have to flush it. i don't think it will mess up the birfs and bearings, but i would make them repack the bearings and birfs for the mess up. 90weight goes in the 3rd member. the inner axle seal should help prevent 90 weight from making it into the knuckles...are you saying that he filled your knuckles with 90 weight?
